Pseudo Random number generator

ASM/8086

Here is a small pseudo random generator. I found it on Andrew Griffinis homepage, but I seem to have misslaid his e-mail and homepage address.

;
; pseudo random number generator
;
; input:
;   bp = seed (!=0)
;
; output:
;   ax = random word
;
; destroys:
;   bp
;   flags
;

	mov     al,16
r_loop: rol     bp,1
	jnc     r_skip
	xor     bp,0ah

r_skip: dec     al
	jne     r_loop
        mov     ax,bp

One improvement that can be done is to replace store BP someway so you can reuse it later in the random routine.

Max McGuire has submitted a new version (note that in order for this version to run on a 286 and below, FS has to be replaced with another segment register):

I'm submitting to you an alternative pseudo random generator that I found in the source for the intro Chaos by Consub of CSB. Here's his original code:


        mov     ax,fs
        mov     bx,13
        mul     bx
        xchg    ah,al
        mov     fs,ax

I kept the same basic idea, but optimized (at least I think I optimized) this code for speed by making a few changes (I also changed the seed from fs to dx): mov bx,dx shl dx,2 add dx,bx xchg dl,dh
I don't know if this algorithm generates random numbers that are uniformly distributed between 0 and 65535.

Gem writers: Andrew Griffini
Max McGuire
last updated: 1998-03-16